Video cameras of conventional structure are provided with various functions to improve their usability such as an automatic focus (AF) function and an automatic exposure (AE) function. While basic control mechanisms of such focusing control and exposure control are automated by known arts, there still are attempts to develop high-level control of such functions. For example, as for the automatic focusing function, focusing on the object when the object is a human being has been made more reliable by detection of the portion of skin-color. As for automatic exposure control, it has become possible to achieve exposure "control suitable for each object" by performing such control as to weighting a portion of the video signal. Such controls are disclosed for example in Japanese Laid-open Patent Application No. 2-214272 and Japanese Laid-open Patent Application No. 3-19476.
However, the automatic focusing control function and the automatic exposure control function provided for conventional video cameras have not always been such as to ensure that the picture taking is always done as intended by the camera operator. For example, as to auto focus control it sometimes occurs that a body in the foreground or background, which is not aimed at by the camera operator, is brought into focus. As to the automatic exposure control, it sometimes occurs, in the case of excessive forward light or the case of back light, that a suitable exposure is not obtained for an object aimed at by the camera operator and, hence, whitening or blackening is caused.
Further, as an apparatus for extracting the portion of an object from a video signal, there has been known a chroma key apparatus as for example, disclosed in Japanese Patent laid-open Application No. 4-3155. In the chroma key apparatus, the background portion in a single color is extracted from a chrominance signal and, thereby, the portion of the object is separated from the portion of background.
However, in order that the portion of the object is extracted in the above described conventional apparatus, it is required that the background is provided in a single color. Therefore, there has been a problem that the apparatus can only be used in a limited environment such as a studio. There has also been such a problem that it becomes difficult to extract an object in stabilized conditions when changes in illuminance are produced or shadows are cast on the background.